The invention relates to a method of producing a progressive spectacle glass as well as to a corresponding progressive spectacle glass.
Progressive spectacle glasses are distinguished by the fact that they have an area for looking into the distance called a far focusing range and an area for seeing nearby called a near focusing range, these areas being connected with one another by a so-called progression zone. In the progression zone, the effect of the spectacle lens increases from the value of the far reference point BF to the value of the near reference point BN situated in the near area along a helical line which is called the main line. The effect difference between the far and the near reference point is called addition.
As a rule, the far focusing range is arranged in the upper area and the near focusing range is arranged in the lower area of the usage position of the spectacle lens. Such progressive spectacle glasses are well known in the state of the art. Only as an example, reference is made to International Patent Application WO 01/81981 of Rodenstock GmbH, München.
As a rule, such progressive eye glasses have, in addition to the initially mentioned far and near reference point, a prism reference point and a centering point. Concerning the terminology and definition, reference is made here to the above-mentioned International Patent Document WO 01/81981, in which the far, near and prism reference point and the centering point represent the generally customary names also used in EN Standard ISO 13666. In the far reference point BF, the far focusing effect, that is, the spherical and/or cylindrical effect of the spectacle glass, is reached. In the near reference point BN, the near effect, that is, the far effect plus the addition, is reached. In the prism reference point, the prismatic effect, that is, the prescribed prism and the thickness reduction prism, is reached.
The centering point BZ is used for centering the spectacle glass and thus represents that point which defines the local position of the spectacle glass with respect to the eye. As a rule, a progressive spectacle glass is centered in front of the eye such that, when the position of the head and body is normal, the spectacle glass, in the case of the so-called zero viewing direction (that is, when the viewing is horizontal), is positioned in front of the eye such that the centering point is situated in front of the pupillary center of the eye.
In patent literature, different terms are partly used for the same points. Thus, in European Patent Document EP 0 911 670 B1, the terms “reference point for the far vision, reference point for the near vision and mounting cross” are used. However, these terms have the same meaning.
As a rule and for the purposes of this application, the reference points have the following heights in vertical sectional views through the spectacle glass; that is, y-coordinates in a projection onto an xy-plane, Far reference point BF y=8 mm, centering point BZ y=4 mm, prism reference point y=0 and near reference point BN y=14 mm. In this case, the so-called horizontal line H of the glass is used as the zero point, the spatial position and direction of the horizontal line H usually being defined by permanent markings which are typically situated at a distance of 17 mm laterally of the main meridian. In the center between the permanent markings on the horizontal line of the glass, the glass center is situated, which in most cases (glasses not predecentered) is the geometrical center of the surface of the unframed glass. In this case, the glass center point coincides with the prism reference point.
Tests have shown that the main viewing direction as a rule deviates from the zero viewing direction, specifically by 5 to 10 degrees downward. This corresponds approximately to a y-coordinate of from 2 mm to −1 mm. Again, the main viewing task, as a rule, is in the distance.
It had therefore already been recognized in the International Patent Application WO 01/81981 of Rodenstock GmbH that it is advantageous for the refraction value to not start to rise directly below the far reference point BF, as otherwise often customary, but only later. Thus, it becomes possible by means of this known spectacle glass to still see into the distance also in the main viewing direction, under certain circumstances, while utilizing the depth of focus. In the case of other conventional progressive spectacle glasses, such as in the embodiments of European Patent Document EP 0 911, 670, this is as a rule no longer possible. In the case of the above-mentioned patent document (compare FIGS. 6 and 9), a fogginess of 0.3 dpt already exists in the main viewing direction, which can be compensated only under the best light conditions and contrast by the depth of focus (approximately +/−0.3 dpt).
Fortunately, the human eye only has a small aperture which varies between 2 and 7 mm. However, since the human eye itself has greater errors of a higher order, the human visual system has also superimposed a “sensory aperture” on the physical aperture. This phenomenon, which is known as the Stiles-Crawford effect, is caused in that the cones—like optical waveguides—are oriented to the pupillary center and are therefore clearly more sensitive to rays coming from there. This results in an effective opening of the pupil of only 2 to 5 mm.
It is an object of the invention to indicate a method of producing a progressive spectacle glass which, while taking into account the typical ordering and production sequence, regularly results in a progressive spectacle glass which has improved optical imaging characteristics for the ordering customer and is particularly less sensitive with respect to refraction errors, particularly positive refraction errors.
This object is achieved by of a method which comprises the following steps:                defining an ordering value for the average use value in the far reference points BF of the progressive spectacle glass;        calculating the progressive spectacle glass while taking into account a calculation value of the average use value in the far reference point BF, the calculation value having a negative desired refraction deviation between 0.03 DPT and 0.2 dpt in comparison to the ordering value in the far reference point BF; and        producing the calculated progressive spectacle glass.        
The negative desired refraction deviation is preferably between 0.08 dpt and 0.12 dpt. In the case of the method according to the invention for producing a progressive spectacle glass, the calculation of the progressive spectacle glass is therefore not based on the ordering value of the average use value in the far reference point BF, but on a so-called calculation value which, with respect to the ordering value, has a negative desired fraction deviation. In other words, the calculation and optimization of the progressive spectacle glass does not start with the ordering value of the average use value in the far reference point BF prescribed for the wearer of the spectacles but a calculation value which deviates therefrom and which is reduced by a predetermined desired refraction deviation with respect to the ordering value. The calculation and optimization step therefore takes place on the basis of an average use value in the far reference point BF which does not correspond to the prescribed median use value.
However, surprisingly, this introduction of a negative desired refraction error in the far reference point BF in the calculation step regularly results in a progressive spectacle glass which has better optical imaging characteristics for the wearer of the spectacles while taking into account the typical ordering and production process. The obtained progressive spectacle glass according to the invention proves to be less sensitive to small refraction errors, particularly positive refraction deviations.
The average use value D, in the sense of this invention, is the average value of the reciprocal values of the image-side distances S′1 and S′2 (between the back lens and the image minus the object distance, thus the object-side distance S, wherein the following applies:
  D  =                              S          ⁢                                          ⁢          1          ⁢          _                +                  S          ⁢                                          ⁢          2                    2        -    S  
In other words, according to the production method of the invention, the calculation value on which the calculation or optimization is based is reduced with respect to the ordering value of the refractive power in the use position in the far reference point BF of the progressive spectacle glass by a predetermined negative desired refraction deviation between 0.03 dpt and 0.2 dpt. Thus, the calculation or optimization step is based on a calculation value of the average use value which nominally for the ordering wearer of the spectacles has a negative desired refraction error of a predetermined amount. The refraction value distribution, on which the calculation and optimization step is based, may, for example, be as in International Patent Document WO 01/81981.
According to a preferred embodiment of the method according to the invention, the step of calculating the progressive lens or spectacle glass takes place by taking into account a calculation addition which is increased at least by the amount of the negative desired refraction deviation in the far reference point in comparison with the ordering addition. Thus, the average use value (or the refraction value in the use position) in the near reference point BN, on which the calculation and optimization step is based, is, for example, equal to the prescribed or ordered average use value in the near reference point BN. For this purpose, the calculation addition on which the calculation step is based is increased by that amount by which the effect in the far reference point was nominally reduced.
According to a particularly preferred embodiment of the method according to the invention, the calculation addition is increased with respect to the ordering addition by the sum                of the amount of the negative desired refraction deviation in the far reference point BF and        of a positive desired refraction deviation between 0.02 dpt to 0.1 dpt, preferably 0.05 dpt.        
Thus, the calculation step of the progressive spectacle glass takes place on the basis of (calculation) refraction values in the use position, which differ in the far reference point as well as in the near reference point from the prescribed (ordering) values. Thus, with respect to the ordering values in the far reference point, there is nominally a negative refraction deviation and, in the near reference point, there is nominally a positive refraction deviation.
The recognitions and motives on which the introduction of desired refraction deviations in the calculation step according to the invention are based, will be explained in detail below.
Preferably, the step of calculating the progressive spectacle glass or lens while taking into account a predetermined desired refraction error takes place on the main line as a function of the y-coordinate along the vertical section of the spectacle glass. Thus, according to this particularly preferred embodiment, the calculation of the progressive spectacle glass takes place while considering a predetermined desired refraction error along the main line or of the main meridian of the spectacle glass, the desired refraction error being a function of y (that is, of the vertical axis). In this case, the predetermined desired refraction error is preferably set such that, in the far reference point, for the calculation value of the average use value, a negative desired refraction deviation is obtained with respect to the corresponding ordering value and, in the near reference point, a positive desired refraction deviation of the calculation value is obtained with respect to the corresponding ordering value. Particularly preferably, in the case of such a calculation or optimization, a so-called double asymptotic function for the desired refraction error is used as a function of y of the form:
      f    ⁡          (      y      )        =      b    +          a      ⁢              a                  1          +                      3                                          c                ⁡                                  (                                      y                    +                    d                                    )                                            ⁢              m                                            +                  ∑        i            ⁢                          ⁢              giy        i            wherein a, b, c, d, m and g1 are constants. The constants may, for example, assume the value a=0.125 dpt, b=−0.125 dpt, c=−0.5 dpt, d=1 mm, m=1.3, i=0. Likewise, it is conceivable to use cubical or higher-grade spline functions or other suitable functions.
The step of calculating the progressive spectacle glass preferably takes place such that the average use value of the produced spectacle glass increases as little as possible in the case of a horizontal viewing deflection in the far range. The average use value of the produced spectacle glass at the height of the far reference point in the case of a horizontal viewing deflection preferably increases by less than 0.25 dpt, preferably by less than 0.15 dpt, in comparison to the average use value in the far reference point. In particular, the calculation step can be implemented such that, when an (additional) refraction error of +0.2 dpt is superimposed (for example, because of manufacturing fluctuations), the far range is reduced by not more than 5%, preferably by not more than 3%.
According to another aspect of the invention, a progressive spectacle glass is suggested which has a far vision part with a far reference point, a near vision part and a progression zone, the progressive spectacle glass being designed such that its calculation takes place while taking into account a calculation value of the average use value in the far reference point, the calculation value having a negative desired refraction deviation of between 0.03 dpt and 0.2 dpt with respect to a predefined ordering value of the average use value in the far reference point.
The negative refraction deviation is preferably between 0.08 dpt and 0.12 dpt. The progressive spectacle glass is preferably designed such that its calculation takes place while taking into account a calculation addition which is increased at least by the amount of the negative desired refraction deviation in the far reference point in comparison to the ordering addition.
The calculation addition is preferably increased with respect to the ordering addition by the sum                of the amount of the negative desired refraction deviation in the far reference point and        of a positive desired refraction deviation between 0.02 dpt to 0.1 dpt.        
According to another aspect of the invention, a progressive spectacle glass is suggested which has a far vision part, a near vision part and a progression zone, the progressive spectacle glass being designed such that, when a refraction error of +0.2 dpt is superimposed, the far range is reduced by not more than 5%, preferably by not more than 3%.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.